Multiple frequency modulation system



Nov. 10, 1942.

A. N. GOLDSMITH Filed Jan.

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1 7 FREQUENCY 10 1/ 4 14 WAC/(GROUND S/GNAL MODULATION CARR/ER DEV/ATIONAPPROX/MA7'E FREQUENCIES AMPL.* FACTOR FREQ. BAND PICTURE -4500000- I004,500,000 LINE SYNCl-l. 13,230 5 5 140,000 FIELD-SYNCH. 60*- x l5 5"'/40,000* Sou/v0 -/2,000- '80 5 140.000* mrmm/wo-mmoz 0 20 5 5 140,000

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A. N. GOLDSMITH MULTIPLE FREQUENCY MODULATION SYSTEM Filed Jan. 22, 1941Nov. 10, 1942.

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VIDEO pm-kfllps AMPLIFIER Ll SYN- SMNAL AMPLIFIER PuF/ER AMPLIFIERCONTROL FM TRANSMITTER AMPLIFIER MODULATOR SOUND PICK-UP 4 Sheets-Sheet4 WATTS w INVENTOR.

ALFRED N. GOLDSMITH ATTORNEY.

Patented Nov. 10, 1942 Mme MULTIPLE FREQUENCY MODULATION SYSTEM AlfredN. Goldsmith, New York, N. Y.

Application January 22, 1941, Serial No. 375,438

17 Claims.

My present invention deals with, and has for one of its objects, theprovision of improved methods for multiple transmissions of relatedsignals utilizing frequency modulation in whole or in part for suchtransmissions, and with the selection of transmission constants for mosteffective and reliable reception.

The invention includes the improved transmission of a multiplicity ofrelated signals which, in general, co-act at the receiving station toform the complete received signal or signals. Further, according to thisinvention at least one of such multiply-transmitted signals istransmitted by frequency modulation; any or all of the remainder may betransmitted either by frequency modulation or by amplitude modulation.The invention applies equally, with obvious modification, to phasemodulation or combinations of amplitude, phase and frequency modulationof any desired types.

As examples of multiple transmissions or groups of signals co-acting, asstated above, to produce the complete received signal, there may bementioned the following (although any other types of multiple andassociated signals fall Within the scope of the invention) (a)Telephonic transmission with indicial or auxiliary signals controllingvolume expansion or contraction, audio frequency characteristic or thelike;

(1)) Facsimile transmission involving the picture or video signal, andalso the indicial or synchronizing signals. These synchronizing signalsmay be exclusively line-synchronizing signals, or they may include aswell page or sheet syncronizing signals;

Facsimile and telephony. This multiple transmission is similar to (b)above except that there is an added further signal which may be, forexample, speech explanatory of the facsimile pictures which are beingtransmitted, or music suitably accompanying such pictures;

(d) Television signals which include the picture or video signals, theline-synchronizing signals, the field-synchronizing signals, and thebackground-control signals. The last three mentioned signals hereinagain are the indicial or auxiliary signals;

(8) Television and telephony. This well known type of transmission issimilar to (a) above except that there is an added sound signal relatedto and forming a part of the combined television-telephone transmission.

In each of the above illustrative transmissions of multiple signalsthere are various types of sigsponding signal.

nalswhich should have, for balanced reception, equal reliability andclarity in every part of the reception, and with an equal or balancedcontribution by each component signal of the multple signal group to theresulting conjoint reception. To accomplish such balanced reception orbalanced contributio of each of the component signals to the final andconjoint result, each of such components should have transmissionparameters adapted to the purpose. It is a feature of this inventionthat the selection of these parameters for frequency modulationtransmissions, alone or in association with amplitude modulatedtransmission, shall be such as to give balanced contributions from eachof the signals. The underlying reason for this is that, in a multiplereception, it is not desirable that some of the included signals shallbe highly reliable while others shall be relatively unreliable incertain portions of the service area.

To be more specific, the selection of the parameters for agiven signalforming one of the multiple group of associated signals is determined byconsidering the following characteristics of the surrounding individualsignal:

(a) The extent or importance of its contribution to the conjoint signal.Some signals must be substantially perfectly received for satisfactoryoperation while others will give tolerable reception despiteconsiderable leeway in the quality of the reception thereof.

(b) Sensitiveness of the received signal of a particular type to naturalor man-made disturbances of reception thereof.

(0) Susceptibility of each type of signal to minor variations or errorsin the receiving equipment constants, or changes in such constantsduring the use of the receiver (e. g., because of heating of thecomponent parts of the receiver and consequent changes in. theirelectrical constants or electrical changes resulting from variations inthe voltage of the power supply).

(01) The inherent width of the frequency band corresponding to themodulation of the corre- For example, for a video signal the band isextremelywide, whereas for a background control signal the band is verynarrow.

(e) The power of the transmitter for that particular signal, whichcorresponds in general to the corresponding carrier amplitude, thepercentage of modulation, or both. In all of the following it is assumedthat modulation is used unless otherwise stated.

It has heretofore been customary to select the operating parameters foreach of the component signals of a multiple transmission in such fashionthat the signal-to-noise ratio at the receiver was as nearly as possiblethe same for each of the component signals. This has been based on theassumption that the signal-to-noise ratio determines absolutely thedesired utility of the signal. In the present invention it has, however,been postulated and explained that the overall reliability factor ofeach component signal, as herein described, is the correct criterion ofthe utility of that signal. Therefore, since the ideal multiple-signalcircuit should have equal utility for each of the received componentsignals, it follows that the overall reliability factor of each of thecomponent signals should be the same and that the circuit parameters foreach of the com-' ponent signals should be correspondingly chosenaccording to that criterion. Further, it should be noted that since thesignal-to-noise ratio for each component signal is only one ofthefactors controlling the overall reliability factor for that signal(and sometimes by no means the most important one under practicalworking conditions),

the operating results obtained by adopting the overall reliabilityfactor as the criterion for selection of the component-signal circuitparametersare not only diiferent-from those which would result fromconsidering only the signal-to-noise ratio as the criterion, but arealso, markedly superior in utility thereto.

From the preceding, it will be seen the objects of this invention is theproduction of max mum reliability of reception not of a single s gnal,but of a multiple associated group of signals arran ed toco-act. 1Another object of. the invention is theappropriate selection ofparameters for each of the in-.

dividual si nals of a multiple transmission to produce balancedreception wherebyeach ofthe component si nals contributes an equal ,orbalanced portion to the reception- I In this invention the parameterswhich are selected for the control of signal reliability .andcontribution are the individual carrier amplitudes and the individualdeviation factors of ,those particular si nals transmitted by frequencymodulation. It is not necessary herein to discuss.

frequency-modulation methods in detail since these a e well known in theart.

To illustrate the invention more fully, there have been selected twopossible methods of produc ng such multiple signal transmissions withbalanced reception of each of the signals. The two cases hereindiscussed are on somewhat different bases and are: 1 1

(A) A system for multiple transmission wherein all signals must havefrequency bands capable of accommodation within a specified and limitedchannel band width. As an example of this, the present invention hasbeen applied to a televisiontelephone transmission restricted to thepresent G-megacycle channels. This is set forth in Figure 1 and table 1.

(B) Systems for multiple transmission wherein there is no particularlimitation to available channel width "for accommodation of the requiredfrequency bands, but wherein extreme reliability and balance ofreception, as defined above, is a controlling factor. As an example ofsuch asystem, there may be selected, as illustrated in Figure 2 andtable 2, a television-telephone channel in the micro-wave regionoccupying,a.channel or band width of about 30 megacycles and intendedfor utmost reliability of rethat among ception, either by the public orin the individual stations of a radio television relay network.

Another example of this second type of system (B) would be a micro-wavetelevision-telephone transmission, with the pictures in full color. Toanticipate slightly, it is obvious that any special indicial signalsrequired to control color in such a transmission must have extremereliability in order to insure precision in the color rendition. Thus,the necessity for accurate background control in black and whitetelevision transmissions is far less than the need for accuratebackground control in color television. Accordingly, the indicialsignals related to color rendition in such a multiple transmission musthave high reliability "and therefore should be given either greatercarrier amplitudes, higher deviation factors for frequency modulationtransmission, or both. More specifically, if a tricolor additivetelevision transmission is involved, the reliability of each of thethree component color transmissions (blue, green and red, respectively)should be related to the delineatory capabilities of the correspondingcolor. Thus, the blue transmission controls (blue having the maximumdelineatory capabilities) should be of the highest reliability, whilethe green transmission contributory signals (the green transmissionhaving intermediate delineatory capabilities) may have slightly lowerreliability, and the least acceptable reliability is re-' quired for thered component contributory signals (which have the least delineatorycapabilities). This illustration is given to indicate the method wherebyany multiple transmission is analyzed and each portion of suchtransmission is then given a suitable parameter, including particularlydeviation factor and carrier amplitude for frequency modulationtransmission, consistent with and required for its reliable reception.

As already indicated, particular examples of systems (A) and (B) aboveare shown on the accompanying drawings, system A being outlined inFigure l and table 1, and system B in in Figure 2 and table 2. Figs. 3and 4 show schematic diagrams of apparatus employed. Each of these is,as stated, a television-telephone transmission since this affordsreadily a practical group of multiply transmitted component signals. Intable 1 are listed under the column signal the five component signals.In the next column are given the ranges of modulation frequenciesrequired for the corresponding purpose or signal. This column requiressome additional explanation, While the line-synchronizing signal isderived from and has an inherent frequency of 13,230 cycles per second(in the case of the illustratively selected i li-line (SO-field persecond television transmission), it may or may not be necessary totransmit the harmonics of the line-synchronizing frequency of 13,230cycles per second in order to secure the brief impulsive wave shapewhich is ultimately desired. Of course, alternatively an actualsaw-tooth deflection wave of that frequency may be transmitted, or apure alternating current of that frequency may betransmitted and causedto trigger an impulse generator at the receiver which controls thesaw-tooth horizontal or line deflection generator. herein, none of whichaffect the general basis of this. invention. The field-synchronizingfrequency is 60 cycles per second and similar remarks apply to theinclusion or non-inclusion of the harmonics of the 60 cycles in themodulation of the transmission. As a matter of fact, in the exampleshown in table 1, all the'sign'als except casting orpoint-to-pointdirectionalcomrnunica the picture signal or frequencymodulated transmissions are on a single carrier andwith the sameillustrative deviation factor offive, but with different percentages ofmodulation. The picture signal itself is shown as amplitude modulated inFigure 1 and occupies the band I, 8, 9, ll), located asymmetricallyrelative to the carrier frequency l5, the-system being the well knownvestigial side-band amplitude modulated transmission. In Figure 1, 2represents the sound carrier percentage of modulation, 3 represents thefield-synchronizing signal percentage of modulation, and 4 and 5 theline synchronizing and background control percentages of modulation.These are all relative values and should not add to more than 100% atany giventime. However, in the example shown it is assumed that all fourof these signals will not reach 100% modulation simultaneously and thattherefore there is slight leeway available.

In the third column of table 1 are, in fact, given the correspondingcarrier amplitudes (for the picture signal) or percentage of themodulation (for the other four signals).

In the fourth column of table 1 are listed the deviation factors, whichare identical for the last four signals. There is, of course, nodeviation factor for the amplitude. modulated picture signal. for eachof the signals is as shown in the fifth column of table 1.

In Figure 1, ll, l2, [3 M show schematically the frequency band occupiedby the sound signal and the video or picture indicial signals asindicated-in table 1. It will be noted that the picture indicial signalswhich must have a high degree of reliability to give proper lineinterlacing, and faithful picture reproduction, are associated with thesound carrier and transmitted by frequency modulation, This constitutesan improvement in reception results.

It is only necessary to point'out finally that, in order to avoidoverlapping modulation frequencies, the field frequency is not sent, butrather a field synchronizing signal of sixty times onehalf or 30 cyclesper second. This can be utilized at the receiver in various simple waysto produce the desired fill-cycle field frequency. Thus, a frequencydoubler can be employed at the receiver or, alternatively, the 30-cyclesignal can be subjected to whole wave rectification, thus makingavailable sixty half-waves per secondv each of which may be used forfield synchronizing purposes. 1

Figure 2 and table 2, forming part thereof, illustrate, an example ofsystem B referred to above. The table is self-explanatory in the lightof the previous explanation of table 1. It will be noted from Figure'2and table 2 that the method differs from Figure l and table 1 in that:(a) the picture transmission is accomplished by frequency modulation forincreased reliability, (b) the last four signals (picture-indicial andsound signals) are each sent on their own carrier, and (0) each of thefive signals has a selected carrier amplitude and deviation factor whichis illustratively chosen to yield an approximation to balanced receptionof the conjoint signal.

It will be noted that the exact values for the quantities in columns 3and 4 of table 2 of Figure 2 will vary with the factors statedhereinbefore. Among other things, also, the optimum overall reliabilityfactor will vary with the type of service as, for example,non-directional broad- The approximate frequency band required tion. I v

This overall reliablity. factor for accomplishingv balanced'reception orbalanced'contribution of each of the component signals to the final andconjoint result maybe expressed inversely in terms of the number offailures of the circuit to function in one hour, or ten hours, or onehundred hours, or any other thoughtfully selected period.Illustratively, supposetha't some form of control signal were beingtransmitted and that 7 its effect normally was a perfectly definite one.

Clearly, according'to the preceding criterion, a circuit and itsterminal equipment which gave, say, twenty failures to operate in onehundred hours would have half the overall reliability factor of acircuit which gave only ten failures to operate in one hundred hours ofoperation.

Alternatively, the overall reliability lfactor might be defined in termsof the ratio of the time during which the circuit was operated (foralong period of operation which would give a fair sample of all normalor even special conditions that might be encountered) to the time duringwhich the circuit failed or was inoperative. Thus, if in one thousandhours of operation the circuit were inoperative three minutes in theaggregate, the reliability factor might be taken as one thousand timessixty divided bythree, or twenty thousand. It is, not necessary here toselect any particular one of a number of rational and useful definitionsfor the overall reliability factor. The illustrative and alternativedefinitions given above suificiently indicate the meaning and purpose ofthe term. All that is required in the choice of the operating constantsof systems covered by this invention would be that the reliabilityfactor of each of the individual signals is substantially the same. Thatis, there should be no more interruptions of service or functioning in agiven period of time of any one of the signalslisted in tables 1 and 2,forming part of Figures 1 and 2; or alternatively the ratio of operativetime for any one of these signals to inoperative time of the samesignal, over a long and typical period of time, should be the same foreach and every one of the signals.

Reverting again to Figure 2 and table 2 forming part thereof, it is tobe noted that the video carrier is swung between the frequency limits 22and 25 so that the picture signal may be represented by the rectangle22, 23, 24, 25. At the receiver the band pass characteristic should bechosen so as to pass not only the band of frequencies 22-25 for thepicture, but preferably should be made wider; for example, by twice thehighest video modulating frequency in order to take care of the sidebands just outside of the frequency range through which the carrier isswung. Thus, the frequency range 2225 of Figure 2 may not represent theexact channel employed, but merely the limits through which the videocarrier frequency is swung.

Numerals 26, 35, All and Q5 of Figure 2 represent additional carrierswhich are frequency modulated in accordance with the indicial signals.-

As illustrated, the amplitudes of these auxiliary carriers and theirfrequency deviations are ad- --justed in accordance with the principlesof this invention. As indicated, the background carrier 26 is swungthrough a range of frequencies from 27 to 30; sound carrier All is giventhe relative amplitude shown and is swung over a range of frequenciesfrom 36 to 39; the field synchronizing impulses are impressed on thecarrier which is swung in frequency over the range 31 to 34;

and the line synchronizing impulses are. impressed on still anothercarrier 45 occupying the band of frequencies from 41 to 44. Typicalrelative amplitudes and frequency deviations for the system depicted inFigure 2 are outlined in greater detail in table 2 and. are shownschematically (not to scale) in the drawing of Figure 2.

That is, since Figure 2 is schematic and not to scale, the relativeproportions of the various rectangles are only indicative of, or roughlyapproximate of, the frequency and amplitudedomains occupied by each ofthe component signals. It should be noted that 21-30 is the backgroundcontrol signal, and occupies about 10 2 30 or 600 cycles, and has anamplitude of 5. 3l34 represents the field synchronizing signal also, andhas a band width of 10 2 60 or 1200 cycles (neglecting harmonics), andan amplitude of 10. 36-39 is the sound signal, and has a width of 215,000 or 150,000 cycles, and an amplitude of 20. signals, and has awidth of 4 2 13,230 or about 106,000 cycles, and an amplitude of 5.

Figure 3 is a schematic diagram of transmitting apparatus operating inaccordance with Figure 1 and table 1. The transmitter TRI, which sendsout the video signal, may be either of the frequency or amplitudemodulated type. It is noted that in Figure 1 and table 1, an amplitudemodulated transmitter is specified, but the type 'of modulation isoptional and does not affect the validity of the method describedherein. The integrating video pick-up IV comprises a photocellarrangement used to measure the average brightness of the scene which isto be transmitted so that an appropriate background control system,expressive of this average brightness, maybe transmitted. In Figure 3,therefore. the integrating video pick-up IV is shown connected to thebackground control BC.

The outputs, respectively, of the line synchronizing signal generatorLS, the field synchronizing signal generator FS, the background controlBC, and the sound pick-up SP (essentially a microphone) are connected toadjustable amplifiers A2, A3, A4, A5 whereby the gain of the waves fedto the mixer amplifier MA is controlled. In this Way, the respectivefrequency deviations of the waves fed to and radiated by the antenna AT2from the frequency modulation transmitter TR2,

controlled by modulator M2, are also controlled. That is, asillustrated, the outputs of amplifiers A2. A3. A4 and A5 are passed intothe mixer amplifier MA which in turn controls the modulator M2 of thefrequency modulation transmitter TRZ. Amplifier Al and modulator Ml areprovided, as illustrated, for the video pick-up apparatus VP.

An entirely feasible alternative method would be to have the outputs ofthe four amplifiers A2, A3, A4 and A5 separately modulate differentsmall frequency modulation transmitters and the outputs of each of thefour frequency modulation transmitters would then be combined with orwithout amplification and fed into a single antenna system. This wouldenable different deviation factors to be used for the four signals to betransmitted, each on their own carrier.

At the receiver, which is not shown in the drawings, there would be aconventional frequency modulation receiver which would produce in itsoutput the four signals including the sound signal, and associatedtherewith. The separation of these four signals, once they weredemodulated, could be accomplished either by normal band-pass filtertechnique, or by the usual ll-44 represents the line synchronizing,

method of heterodyning followed by intermediate frequency selection.

Each of the transmissions shown in the attached Figure 4, whichcorresponds in general only to Figure 2 and table 2, may or may not havethe same overall reliability factor. The factors are such that improvedoverall reliability follows as compared to prior art systems. It will beobserved that Figure 4 is somewhat similar to Figure 2, but instead ofusing carrier amplitudes in the ratios given in table 2, I have usedcarrier power in the same ratios. It will also be noticed in the exampleillustrated in Figure 4 that I have used high power and low deviationfactor for the video or picture transmission to minimize channel width.I have used low power and a medium deviation factor for the linesynchronizing signal which is not too critical and does not requireideal conditions for a high overall rehahility factor. I have usedhigher power, and exceptionally large deviation factor, for the fieldsynchronizing signal inasmuch as precision of line interlacing in theresulting picture requires nearly ideal conditions to give a highoverall reliability factor for line interlacing. The background controlsignal is on low power, and has been given a high deviation factor totake care of sudden changes in motion picture or film transmission. Thesound channel has been given medium power and a higher deviation factorthan the picture signal in order to get substantially the same overallreliability factor as the other component signals.

It is to be clearly understood that composite systems wherein amplitudemodulation is combined with either frequency modulation or phasemodulation fall within the scope of this invention.

Also, the criterion for transmission or nontransmission of the harmonicsof the line-synchronizing signal depends on the nature of the receivingcircuit and its operation; that is, whether the said circuit isresponsive to the linesynchronizing signal in such fashion that anaccurately timed response can be secured in such circuit from anincoming synchronizing signal having a given abruptness of rise at itsleading edge (that is, at the inception of such signal). If the circuitwill respond accurately in timing to a synchronizing signal having afairly gradual rate of its rise at its inception, it will not benecessary to transmit the harmonic frequencies of the synchronizingsignalotherwise it may be necessary so to do,

Having thus described my invention, what I claim is:

1. In a signaling system in which a multiplicity of related signalscoact at a receiving point of the system in order to form the completesignal or completed signals transmitted from a transmitting point of thesystem, a plurality of electrical circuits at the transmitting end ofthe systern for generating the series of related component signals, andelectrical wave means to transmit each of the related component signals,the circuits and electrical wave means for each component being arrangedto have parameters related to those for the other signal components, soas to produce substantially identical reliability factors for each ofthe component signals.

2. The system of claim 1, characterized by the fact that means areprovided for transmitting one or more of the signal components byfrequency modulation,

3. A transmitting system for transmitting a multiplicity of relatedsignals, which related signals are all necessary and must 'coact inorder to form the complete signal, comprising aplurality of modulationcircuits, one "for each of the component or related signals, each ofsaidmodulation circuits having .parametersrelated to those of theother'modulation circuits to produce a substantially identicalreliability factor foreach of the component signals, and means for-transmitting the output of'eac'h of said modulation circuits.

4. In a radio system wherein a group of component signals aretransmitted o that by coaction and combination of said component signalsthe whole transmitted signal is reconstructed, a transmitting systemcomprising means for transmitting one of the component signals byfrequency modulation over one channel, and means for transmitting theother components of the signal by independent modulations over otherchannels, the parameters of the modulation circuits being inter-relatedto produce a substantially identical overall reliability factor for eachof the component signals.

5. In a sound-picture system employing a pair of high frequencychannels, means for producing a carrier wave in each channel, means foramplitude modulating one of said carriers with the picture signal, andmeans for frequency modulating the other carrier with thepicture-accompanying sound signal, the parameters of the modulationcircuits being inter-related to produce substantially identical overallreliability factors for the sound and picture channels.

6. A transmitting system for transmitting a multiplicity of relatedsignals, which related signals are adapted to coact in order to form thecomplete signal, a plurality of modulation circuits including at leastone frequency modulation circuit and an amplitude modulation circuit,one for each of the component signals, each of said modulation circuitshaving parameters related to those of the other modulation circuits toproduce a substantially identical reliability factor for each of thecomponent signals, and means for transmitting the output of each of saidmodulation circuits.

7. In a signaling system a first high frequency generator, a second highfrequency generator operating at a different frequency, means formodulating oscillations from the first generator with a picture signalwith one type of modulation, and means for modulating oscillations fromthe second generator with a second signal to accompany the picturesignal but with another type of modulation, and means for simultaneouslytransmitting both modulated oscillations, the parameters of the circuitsbeing related to produce the same overall reliability factors for bothcircuits.

8. In the signaling system of claim 1, a receiver suitable for signalstransmitted therein, said receiver being characterized by the provisionof a filter for each of the component signals transmitted, and means fortranslating the filtered signals in such co-relationship as tore-establish the whole transmitted signal.

9. The transmitting system of claim 3 in combination with a receiversuitable for receiving signals transmitted thereby, said receiver beingcharacterized by the provision of a filter for each of the componentsignals transmitted, and means for transmitting the filtered signals insuch corelationship as to reestablish the whole transmitted signal.

10. In a radio system wherein a group of component signals aretransmitted so that bycoaction and combination .of said componentsignalsthe whole transmittedjsignal is reconstructed, a transmitting systemcomprising means for transmitting one of the component signals byfrequency modulation over one channel, and means for each of thecomponent signals.

11. In a radio system wherein a group of component signals aretransmitted so that by coaction and combination of said componentsignals the whole transmitted signal is reconstructed, a transmittingsystem comprising means for transmitting one of the component signals byfrequency modulation over one channel, and means for transmitting theother components of the signal by independent modulations of differenttypes over other channels, the parameters of the modulation circuitsbeing interrelated to produce a substantially identical overallreliability factor for each of the component signals.

12. In a radio system wherein a group of component signals aretransmitted so that by coaction and combination of said componentsignals the whole transmitted signal is reconstructed, a transmittingsystem comprising means for transmitting one of the component signals byangular velocity modulation over one channel, and means for transmittingthe other components of the signal by independent modulations over otherchannels, the parameters of the modulation circuits being inter-relatedto produce a substantially identical overall reliability factor for eachof the component signals.

13. In a system wherein a plurality of related radio signals are to betransmitted for coaction at a remote receiving point, the method ofoperation which comprises determining the permissible total time offailure of each of the related signals over a protracted period of time,and adjusting the values of carrier amplitude and percentage modulationfor each of the related signals which will give for all related signalssubstantially the same proportion of total time of failure of operationto the time during which the signal component was under observation.

14. In an angular velocity system wherein a plurality of related radiosignals are to be transmitted for coaction at a remote receiving point,the method of operation which comprises determining the permissibletotal time of failure of each of the related signals over a protractedperiod of time, and adjusting one or more of the values of carrieramplitude, percentage modulation and deviation factor for each of the related signals which will give for all the signals substantially the sameproportion of total time of failure of operation to the time duringwhich the particular signal component was under observation.

1-5. In a signaling system according to claim 1, including frequencyselective circuits at the receiving point for the discrimination of thecomponent signals.

16. In a system wherein a plurality of related radio signals are to betransmitted for coaction at a remote receiving point, the method ofoperation which comprises determining the permissible total time offailure of each of the related signals over a protracted period of time,

and adjusting the Values of carrier amplitude and percentage modulationfor each of the related signals which will give for all related signalssubstantially the same proportion of total time of failure of operationto the time during which the signal component was under observation,and. wherein the total value of all percentages of modulation of therelated signals does not exceed 100% at any given time,

17. In a multiplex signaling system wherein the component signals are ofdiverse character and not primarily dependent on the signal-tostatic'ratio thereof in each case for the determination of the overallreliability of operation of the corresponding component signal, aplurality of electrical circuits at the transmitting end of the systemfor generating the component signals, and electrical wave means totransmit each of the component signals, the circuits and electrical wavemeans for each component being arranged to have parameters related tothose for the other signal components, so as to produce substantiallyidentical reliability factors for each of the component signals,

ALFRED N. GOLDSMITH.

